Abstract

A parameterization of line-shaped contrails for use within the framework of a general circulation model (ECHAM) was developed for the first time. Contrail coverage, optical properties and radiative forcing are calculated at any model time step depending in a physically based manner on the respective conditions in the ambient air. In addition, possible effects on atmospheric parameters can be simulated, allowing for the determination of a climate sensitivity parameter especially for line-shaped contrails. Regional contrail cover as well as the large range of simulated optical depth values show a fair qualitative and quantitative agreement with observations.
Sensitivity studies result in a lower global radiative forcing of line-shaped contrails than estimated
by the Intergovernmental Panel on Climate Change (1999). Remaining uncertainties are mainly associated with poor knowledge of microphysical properties such as ice water content, particle shape and size. Considering future changes in air traffic density, and aircraft technology, as well as anthropogenic climate change, an increase of global contrail cover and radiative forcing by roughly a factor of four between 1992 and 2050 is simulated.